It is known that such a slaving chain comprises electronic components which may, in failed mode, generate a spurious signal which can cause the slaved airfoil to oscillate. A phenomenon of this type is called an “oscillatory fault”. A possible cause of the oscillation is the malfunctioning or breaking of a mechanical part of the servocontrol.
It is known moreover that, when an oscillatory fault such as this exhibits a frequency which lies inside the passband of the actuator, it has the effect:                of generating significant loads on the structure of the aircraft, thereby making it necessary to strengthen this structure;        of generating excessive loads in the event that one of the natural modes of vibration of the aircraft is excited (resonance phenomenon, aeroelastic coupling), and this may, in the extreme case, cause damage to the structure of the aircraft;        of accelerating the fatigue of the actuator or actuators used; and        of reducing the comfort of the aircraft's passengers.        
The complete coverage of such oscillatory faults would require overly expensive structural strengthening of the aircraft. In practice, the aircraft is designed to absorb oscillatory faults of a certain amplitude, as a function of frequency. So, monitoring must be put in place to guarantee that the vibrations of the aircraft remain within a predetermined amplitude/frequency envelope.
However, the standard solutions for carrying out such monitoring are highly dependent with respect:                to the hardware used;        to the type of piloting law for the aircraft (function of its flexibility or lack thereof);        to the computer's acquisition and generating system; and        to the fault modes of said computer.        
Consequently, to a particular family of aircraft there corresponds on each occasion a particular standard solution, which has no guarantee of being applicable to another, existing or future, family of aircraft.
Moreover, the standard monitoring solutions generally exhibit restricted coverage, usually carrying out only detection of the oscillations generated by a particular component of the slaving chain.